The stop joints provide a mechanical barrier against the oil or other fluid flow from one section of the cable to another or from one type of cable system to another type.
They are commonly used on medium pressure oil filled or low pressure oil filled cables to avoid unsafe high pressure condition when the cable run profile has a large level variation. In such cases the number of stop joints is determined by the permissible hoop stress in the cable sheath.
Stop joints are also used for connecting different cable systems, such as high pressure oil filled, low pressure oil filled cable or gas cables, etc. The stop joints not only have a large variety of applications, but they also have a large variety of designs. The earliest were made of two inverted terminals in a vertical configuration.
Presently, it is a common practice to use stop joints with porcelain or some type of resin barriers. The barriers can be installed between the two cables or pulled over one or both cable ends, this type being called "stop tubes." The most widely used stop tubes are made of porcelain having a conical shape. Less expensive cylindrical type stop tubes are also known, but they are not used as frequently. This unpopularity is due to their bulky connector arrangement, which is required for bringing the high voltage potential to the outer surface of the stop tube. Furthermore, the stress control of this arrangement is not very effective, and the joint construction is delicate.
Although the stop joint of this invention has a cylindrical stop tube, many of the known drawbacks mentioned above are eliminated. The tube is preferably made of a resin base material, preferably reinforced by fiberglass, paper or other suitable materials, having good electrical and mechanical characteristics, at a considerably reduced cost. The two sealing ends are made of metal and they are glued or cast into the resin base tube. Because the ends are active parts of the electrode system, the size of the electrode is greatly reduced.
The high voltage electrode system consists of an inner electrode at the sealing end of the stop tube, and a conical envelope over the connector. The ends of the conductors of both lengths of cable extend into the connector, but on opposite sides of an inner barrier that prevents flow of oil or other fluid.
Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.